Pseudomonas aeruginosa has innate characteristics of developing resistance. Therefore, it is obligatory to find the new antipseudomonal agents: Zno colloidal nanoparticles (NPs) synthesized via chemical deposition method. Then, TEM, SEM, DLS, and UV-visible were done. Sampling was achieved from not the same sections of infectious unit and then Pseudomonas aeruginosa was isolated from hospital and its antibiotic resistance pattern was determined. Disc diffusion, cavity, MIC, and MBC tests were done. Absorption of UV-visible occurred at about 350 nm. The mid-range of hydrodynamic diameter and the average size of the ZnO NPs were 1.48 um and 5 nm, respectively. Isolated Pseudomonas aeruginosa was resistant to Trimethoprim, Ampicillin, and Nitrofurantoin. The disc diffusion and cavity test of antibiotic-resistant Pseudomonas aeruginosa showed respectively the least sensitivity to ZnO (DIZ = 8 mm and 5 mm) in comparison of standard strain of Pseudomonas aeruginosa (DIZ = 10 mm and 8 mm). According to the results, ZnO NPs could kill all antibiotic-resistant bacteria at a ratio of 1:16 (MBC = 7.5 ppm). However, it was able to eliminate the standard strain of Pseudomonas aeruginosa at a ratio of 1:64 (MBC = 0.937 ppm). This study demonstrated that ZnO NPs have high potential for disinfection of infectious units of hospitals against nosocomial infection – especially by Pseudomonas aeruginosa.